ExceptionExample of propagating and Problem 13 Answer from Review Sheet

exam1/src/exam3/Book.java

 package exam3;
 
-public class Book extends LibraryItem implements Item {
+public class Book extends LibraryItem {
 	public Book(String title) {
-		super(title);
+		super(title, 21);
 	}
-
-	public int getCheckOutPeriod() {
-		return 21; // three weeks
+	
+	protected Book(String title, int checkOutPeriod) {
+		super(title, checkOutPeriod);
 	}
-}
\ No newline at end of file
+}

exam1/src/exam3/DVD.java

@@ -4,7 +4,7 @@ public class DVD extends LibraryItem {
 	private int duration; // duration in minutes
 
 	public DVD(String title, int duration) {
-		super(title);
+		super(title, 7);
 		this.duration = duration;
 	}
 
@@ -12,11 +12,7 @@ public class DVD extends LibraryItem {
 		return "DVD:	" + super.getTitle();
 	}
 
-	public int getCheckOutPeriod() {
-		return 7; // DVDs check out for one week
-	}
-
 	public int getDuration() {
 		return duration;
 	}
-}
\ No newline at end of file
+}

exam1/src/exam3/ExceptionExample.java

+package exam3;
+
+/**
+ * Illustration of exception handling.
+ */
+public class ExceptionExample
+{
+  /**
+   * @param args not used
+   */
+  public static void main(String[] args)
+  {
+    ExceptionExample t = new ExceptionExample();
+    System.out.println("main calling m1()");
+    t.m1();
+  }
+
+  
+  // Called by main()
+  public void m1()
+  {
+    System.out.println("Starting m1 ");
+ 
+    try
+    {
+      m2();
+      
+      // remaining code is not executed if m2 throws an exception
+      System.out.println("Finishing try block of m1");
+    }
+    catch (MyException e)
+    {
+      System.out.println("m1 caught exception: " + e);
+      // if we want, look at the stack trace
+      //e.printStackTrace(System.out);
+    }
+    
+    // we could also catch other exception types
+    catch (NullPointerException npe)
+    {
+      System.out.println("m1 caught a NullPointerException");
+    }
+    
+    // remaining code is still executed if m2 throws MyException,
+    // which we caught and handled above
+    System.out.println("Executing last line of m1");
+  } 
+  
+  // Called by m1()
+  public void m2() throws MyException
+  {
+    try
+    {
+      System.out.println("  Starting m2");
+      m3();
+      
+      // remaining code is not executed if m3 throws an exception
+      System.out.println("  Finishing try block of m2");
+    }
+    finally
+    {
+      System.out.println("  Finally block of m2 executes no matter what");
+    }
+    
+    // remaining code is not executed if m3 throws an exception
+    System.out.println("  Executing last line of m2");
+  }
+  
+  // Called by m2()
+  public void m3() throws MyException
+  {
+    System.out.println("    Starting m3");
+    m4();
+    
+    // remaining code is not executed if m4 throws an exception
+    System.out.println("    Executing last line of m3");
+  }
+  
+  // Called by m3()
+  public void m4() throws MyException
+  {
+    System.out.println("      Starting m4");
+    
+    // throw a checked exception...
+//    System.out.println("      About to throw MyException from m4");
+//    throw new MyException("This happened in m4");
+    
+    // or, throw a runtime exception...
+    //System.out.println("      About to throw NullPointerException from m4");
+    //Object obj = null;
+    //obj.toString();
+    
+    // or, just return normally
+    //System.out.println("      Returning normally from m4");
+
+  }
+}
+
+/**
+ * A simple subclass of Exception.  Note this is a "checked"
+ * exception, since we aren't extending RuntimeException.
+ */
+class MyException extends Exception
+{
+  public MyException(String message)
+  {
+    super(message);
+  }
+  public MyException()
+  {
+    super();
+  }
+}
+

exam1/src/exam3/InheritancePart.java

@@ -20,11 +20,18 @@ public class InheritancePart {
 		// System.out.println(li.getDuration());//Compile error, No getDuration method in
 		// LibraryItem
 		System.out.println(((DVD) li).getDuration());
-		i = b;
-		// b = i;//Compile error, No Downcast
+		i = (Item) b;
+//		b = i;//Compile error, Declared type of i is Item and No Downcast
+		System.out.println(b.getClass() == i.getClass());
+		System.out.println(b instanceof Book);
+		System.out.println(i instanceof Book);
 		System.out.println(i.getTitle());
-		ReferenceBook rb = (ReferenceBook) b;
-		System.out.println(rb.getTitle());
+//		ReferenceBook rb = (ReferenceBook) b;
+//		System.out.println(rb.getClass() == b.getClass());
+//		System.out.println(rb.getClass() == i.getClass());
+//		System.out.println(rb instanceof Item);
+//		System.out.println(rb instanceof Book);
+//		System.out.println(rb.getTitle());
 	//	rb = (ReferenceBook) new Book("Big	Java"); // Exception
 													// ClassCastException Book
 													// cannot be cast to

exam1/src/exam3/LibraryItem.java

@@ -2,14 +2,18 @@ package exam3;
 
 public abstract class LibraryItem implements Item {
 	private String title;
+	private int checkOutPeriod;
 
-	protected LibraryItem(String title) {
+	protected LibraryItem(String title, int checkOutPeriod) {
 		this.title = title;
+		this.checkOutPeriod = checkOutPeriod;
 	}
 
 	public String getTitle() {
 		return title;
 	}
 
-	public abstract int getCheckOutPeriod();
+	public int getCheckOutPeriod() {
+		return checkOutPeriod;
+	}
 }
\ No newline at end of file

exam1/src/exam3/RecursionPart.java

@@ -74,20 +74,16 @@ public class RecursionPart {
 		return number;
 	}
 
-	public static int tryStuff(String text) {
-		int total = 0;
-		int i = 0;
-		Scanner scanner = new Scanner(text);
-		while (scanner.hasNext()) {
-			try {
-				String s = scanner.next();
-				i = Integer.parseInt(s);
-				total += i;
-			} catch (NumberFormatException nfe) {
-				total -= i;
+	public static void mysteryWithoutRecursion(int x) {
+		while (x != 0) {
+			if (x % 2 == 0) {
+				System.out.println(x);
+				x /= 2;
+			} else {
+				x -= 1;
 			}
 		}
-		return total;
+		System.out.println("pooh");
 	}
 
 }